It is common to employ open end and box wrenches, or wrenches having one adjustable jaw member to grip hexagonal bolts or nuts. In the case of open end and box wrenches, they make good contact with the several flats of hexagonal bolts or nuts, but a different size wrench is required for each size of fastener. The adjustable wrenches have disadvantages in that they generally engage only two of the hexagonal bolt/nut flats and, consequently, are subject to slippage about the fastener, they generally require carefully machined screw-type driving surfaces and must be reversed as between fastening and unfastening operations.